qemu.balloon_check: reset the memory to origin value

The memory should be reset to the origin value after
evict or enlarge. So that the next iterations tests can
pass when check memory before test

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
Fix libvirt_xml/vm_xml.

This patch fix define and undefine method in VMXML class to return False
if define or undefine fail.

Fixing the comment of virsh.undefine by the way.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
libvirt.tests: Fix testcases to new XML define-undefine.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #641 from QiuMike/qemu.balloon_check_reset_the_memory_to_origin_value

qemu.balloon_check: reset the memory to origin value
virttest.qemu_vm : add vcpu hotplug

This patch add a function for vcpu hotplug.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
qemu.test : add some test for cpu_hotplug

Add cpu_hotplug test support in autotest.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>